The proposed project is a continuation of an ongoing research grant for the study of the structure and function of isolated sperm membrane autoantigens. This project will biochemically characterize, including amino acid and carbohydrate analysis, modifications that occur to rabbit sperm membrane autoantigens and to RSA-1 in particular after they leave the testis, as they pass through the epididymis, mix with seminal fluid, undergo capacitation and finally interact with the zona pellucida. This project will also: 1) identify the biologically active determinant(s) of RSA-1 and other autoantigens in the fertilization process using monoclonal antibodies, 2) identify extrinsic components which associate with sperm surface autoantigens, 3) isolate a regionally restricted surface domain of the sperm using a monoclonal antibody and 4) investigate the association of sperm autoantigens with antigens of the major histocompatibility complex. The significance of this proposal lies in its long term goal of defining and understanding the structure and function of sperm membrane autoantigens. Sperm autoantigens are important because they function during normal fertilization and because they are responsible for autoimmune reactions to spermatozoa which can lead to infertility and autoimmune disease of the testis.